(1) Field of the Invention
This invention relates to an apparatus for cooling an engine, and more particularly to a partial-boil cooling apparatus in which the combined boiling and cooling action of an additional cooling medium different from a cooling water is utilized for partial cooling.
(2) Description of the Related Art
Heretofore the majority of modern cooling apparatuses for engines are of the type using water as a coolant. This water-cooling type of cooling apparatuses are exemplified by a cooling apparatus shown in FIGS. 4 and 5 of the accompanying drawings FIG. 4 is a vertical cross-sectional view of an engine, and FIG. 5 is a side elevational view of the engine.
In FIGS. 4 and 5, reference numeral 1 designates an engine; 2, a cylinder block partially constituting a body of the engine 1; 3, a cylinder head partially constituting the body of the engine 1; and 4, an oil pan disposed on a lower end of a skirt part 2a under the cylinder block 2. Inside the cylinder block 2, a liner 13 in which a piston 12 is to be slidably inserted is mounted, and the cylinder head 3 is mounted on the upper end of the liner 13 via a gasket 20.
Further, reference numeral 5 designates an intake pipe connected to the cylinder head 3; 6, an exhaust pipe also connected to the cylinder head 3; 7, an intake passage defined by the cylinder head 3 and the inner surface of the intake pipe 5; 8, an exhaust passage defined by the cylinder head 3 and the inner surface of the exhaust pipe 6; 9, an intake valve mounted in the intake passage 7; and 10, an exhaust valve mounted in the exhaust passage 8.
The engine 1 is furnished with an engine cooling apparatus 11 of the water-cooling type. The cooling apparatus 11 generally comprises a water jacket 14 constructed round the cylinder block 2 as well as the liner 13 and the intake and exhaust valves 9, 10 inside the cylinder head 3, a radiator 15 for cooling a cooling water 19 filled in the water jacket 14, and a water pump 16 for causing the cooling water 19 to be forcibly circulated (indicated by arrows in FIG. 5) within the water jacket 14.
The water jacket 14 is connected, for communication, to the radiator 15 via a cooling-water supply pipe 17 and a cooling-water discharge pipe 18. The water pump 16 is disposed between the cooling-water supply pipe 17 and the water jacket 14.
In the cooling apparatus 11, the cooling water 19 cooled in the radiator 15 is forced by the water pump 16 to flow via the cooling-water supply pipe 17 into the water jacket 14, where the cooling water 19 moves about by convection as indicated by the arrows in FIG. 5 to cool heated parts around the liner 13 and the intake and exhaust valves 9, 10. Then the cooling water 19 is returned into the radiator 15 via the cooling-water exhaust pipe 18 for being cooled again. Cooling of the engine is accomplished by this circulation of the cooling water 19.
However, according to the temperature distribution of the cooling water 19 within the water jacket 14 in the above prior cooling apparatus, it is high temperature at the upper or cylinder-head-side part of the water jacket 14 and near the upper part, and the temperature descends gradually toward the skirt part 2a of the cylinder block 2, which is located near the lower part of the water jacket 14. The temperature distribution of the liner 13 also is non-uniform due to the non-even distribution of the cooling water 19. Because of this non-uniformness of temperature distribution, the liner 13 tends to be deformed irregularly, which would be a cause for the increase of consumed lubricant oil and the increase of slapping sound of the piston as well as local contacting of the piston.
For cooling near the skirt part 2a of the liner 13, the water pump 16 must be excessively operated, thus impairing the cooling efficiency.
To this end, an engine cooling apparatus 21 as shown in FIGS. 6 and 7 has been proposed in an attempt to make the temperature distribution around the liner uniform and also to make the cooling effective.
FIGS. 6 and 7 are very identical with FIGS. 4 and 5; therefore the description of various parts is omitted here for clarity, with similar parts being only designated by like reference numerals.
In the cooling apparatus 21, the water jacket 24 is divided into two parts: a forcible circulation part 24a where the cooling water 19 inside is forcibly moved by the water pump 16, and a natural convection part 24b where the cooling water 19 inside is restrained from forcible movement by the water pump 16.
Specifically, as shown in FIG. 6, the water jacket 24 is divided by a communication hole 22 into two parts: an upper part (forcible circulation part) 24a located over the communication hole 22, and a lower part (natural convection part) 24b located under the communication hole 22. As shown in FIG. 7, the cooling water 19 in the forcible circulation part 24a is forcibly circulated by the water pump 16, while the cooling water 16 in the natural convection part 24b is only allowed to move by natural convection as restrained from forcible circulation by the water pump 16 since the natural convection part 24b is partitioned off the water pump 16.
With this arrangement, the cooling water 19 cooled by the radiator 15 is forced by the water pump 16 to flow via the cooling-water supply pipe 17 into the forcible circulation part 24a, where the cooling water 19 moves about by convection as indicated by arrows in FIG. 7 to cool heated parts around the upper portion of the liner 13 and the intake and exhaust valves 9, 10. Then the cooling water 19 is returned into the radiator 15 via the cooling-water exhaust pipe 18 for being cooled again.
To the contrary, in the natural convection part 24b of the water jacket 24, the cooling water 19 having become high in temperature as absorbed the heat from the liner 13 is moved upwardly adjacent to the communication hole 22 by natural convection. Then this cooling water 19 is returned downwardly, as cooled by the cooling water 19 in the forcible circulation part 24a, to cool the liner 13 again.
Thus the forcing of the cooling water 19 is necessary with respect to only a part (i.e., the forcible circulation part 24a); that is, the total sectional area of the circulating path of the cooling water 19 would be reduced so that the circulation speed of the cooling water 19 can increase yet by using the water pump 16 of the same output, thus not only improving the heat conductivity of the circulation system under forcible circulation, but also increasing the cooling capability at the forcible circulation part 24a.
The natural convection part 24b has a heat conductivity lower than that of the forcible convection part 24a, and hence the cooling water 19 inside also would tend to become high in temperature.
Accordingly, the temperature of the cooling water 19 in the water jacket 24 becomes lower near the cylinder head 3 at the upper part of the water jacket 24, compared to the previous arrangement, and becomes higher near the skirt part 2a of the cylinder block 2 at the lower part of the water jacket 24, thus resulting in an almost uniform distribution of temperature of the cooling water 19. Therefore the liner 13 also would be uniform in either temperature distribution or deformation, and so it is expected that the increase of consumed lubricant oil and the increase of slapping sound of the piston as well as local contacting of the piston.
However, merely dividing the water jacket 24 into the two parts, i.e., the forcible circulation part 24a and the natural convection part 24b would reduce the heat conductivity at the natural convection part 24b sharply only to increase the possibility that the liner 13 cannot be cooled all the way down to a desired temperature.